1. Field of the Invention
The present invention relates to a system for managing a layered network which includes an upper layer and a lower layer, and more particularly, to recovery from a fault in a layered network which is configured of different management domains such as the topology, technology (SONET, ATM, IP) and the like.
2. Description of the Related Art
Conventionally, there is a layered network that is configured of different management domains such as the topology, technology (SONET, ATM, IP) and the like. Such a layered network is managed in accordance with individual management policies for respective layers. This is because each layer is implemented by a different technology. Therefore, it is often the case that an upper layer fails to detect a fault that has occurred in a lower layer, and a long time is taken for the upper layer to detect the fault.
In the following, an exemplary fault management will be described for an illustrative upper layer represented by the IP (Internet Protocol) network (layer 3) that has been increasingly utilized in recent years. A router on an IP network periodically exchanges a connection confirmation data packet (HELLO packet) with an adjacent router to confirm that the router is in connection with the adjacent router. In this event, if a fault exists between the routers, the router cannot receive the connection confirmation data packet from the adjacent router.
Generally, the router determines that the connection fails between the router itself and the adjacent router if it does not receive the connection confirmation data packet from the adjacent router within a predetermined time period. In this event, connection rerouting is performed. The rerouting permits the router to transmit data packets, which have been transmitted to the adjacent router, to another router that corresponds to the bypassed one. In this way, the data packets are transmitted to a destination through a bypass route.
In the rerouting, the transfer priority and allocated bandwidth for data packets are set to an alternative router. The settings are performed by an IP layer management system that is triggered by a notice from a router that determines the occurrence of a fault.
The following problem has been encountered in the foregoing system that relies on the connection confirmation data packet to detect a fault and proceeds with recovery processing (the rerouting and the like). Specifically, a fault in a connection of the layer 3 is caused by a failed link (disconnected link) in a lower layer (data link layer: layer 2). This link fault can be detected by the aforementioned system at the layer 3. However, in the layer 3, a transmission interval for the connection confirmation data packet is typically set to several minutes for purposes of limiting the amount of traffic. In addition, a fault may be determined when the connection confirmation data packet cannot be received several times in succession from an adjacent router.
On the other hand, a network on a lower layer (layer 2) is managed and controlled in accordance with a management policy different from that of the layer 3. A link fault is detected in the layer 2 management system. A link fault in the layer 2 is often detected earlier than that in the layer 3 because of the fault detection system in the layer 3 which is configured as described above.
Conventionally, however, the layer 2 and layer 3 are managed by different management systems as mentioned above, so that a link fault detected in the layer 2 is not notified to the layer 3 management system. For this reason, although a link fault has been detected in the layer 2, the layer 3 detects the link fault through a connection fault at a later time.
Also, even when a fault on a link in the layer 2 results in a reduction in the bandwidth, a router can exchange the connection confirmation data packet in the layer 3. Therefore, the router does not recognize the degraded performance (reduced bandwidth) in the layer 2. As such, the layer 3 management system does not take any measures thereto. In this way, the control policy in the layer 3 based on information on the network in the layer 3 fails to accommodate the degraded performance of a link in the layer 2.
The foregoing problems: (1) an excessive time taken to detect a fault on a link (line connection) in a lower layer; and (2) the inability to accommodate the degraded performance of a link (line connection) in the lower layer, have remained as general problems in a layered network in which the upper layer and lower layer are managed and controlled based on different policies independently of each other.